1. Field of the Invention
The present invention relates to a semiconductor light emitting device having electrodes formed of metallic material on surfaces of a semiconductor lamination. In addition, the present invention also relates to a method for producing the above semiconductor light emitting device.
2. Description of the Related Art
The semiconductor light emitting devices each include a semiconductor lamination formed by successively stacking an n-type semiconductor layer and a p-type semiconductor layer on a substrate so as to emit light when the semiconductor lamination is energized. Electrodes needed for the energization are formed on the semiconductor lamination, and the surfaces of the electrodes are covered by protection films of insulating material preventing occurrence of a short circuit. In the manufacture of such semiconductor light emitting devices, production methods in which multiple elements are concurrently produced are used. In such production methods, first, a semiconductor lamination is formed by successively stacking an n-type semiconductor layer and a p-type semiconductor layer on a substrate. Then, structures of multiple semiconductor light emitting devices are formed on the semiconductor lamination in a matrix arrangement. Finally, the substrate on which the above structures are formed are separated into the individual semiconductor light emitting devices by cleaving the substrate (for example, see JP 2000-091636 A or JP 10-173229 A).
According to another known technique different from the above semiconductor light emitting devices, a single light emitting device is produced by arranging multiple blocks of semiconductor laminations (semiconductor lamination blocks) on a single substrate and connecting the multiple blocks in series (for example, see JP 10-107316 A or JP 3117281 U). In the above arrangement, each of the multiple semiconductor-lamination blocks corresponds to a single conventional light emitting device. Therefore, the quantity of light| emitted by the light emitting device constituted by multiple semiconductor-lamination blocks can be equivalent to the quantity of light emitted from an aggregation of multiple separate light emitting devices. The above light emitting device constituted by multiple (e.g., four) semiconductor-lamination blocks can be produced as follows. That is, first, semiconductor laminations are formed by successively stacking an n-type semiconductor layer and a p-type semiconductor layer on a large-size substrate. Then, multiple semiconductor-lamination blocks are formed in the above semiconductor lamination in a matrix arrangement. Subsequently, the four semiconductor-lamination blocks, which are to finally constitute a light emitting device, are electrically connected. Finally, the substrate is divided into portions respectively corresponding to the four semiconductor-lamination blocks.
Further, JP 2008-227018 A discloses a method for producing a semiconductor light emitting device. In the method described in JP 2008-227018 A, multiple semiconductor light emitting devices are formed in a matrix arrangement on a single substrate, and the substrate is finally cleaved into the individual semiconductor light emitting devices. Specifically, a connection part making a short circuit between an n-type semiconductor layer in a semiconductor light emitting device and a p-type semiconductor layer in an adjacent semiconductor light emitting device is formed, and metal electrodes are formed while the above short circuit is maintained. Thereafter, the n-type semiconductor layer and the p-type semiconductor layer are electrically separated by cutting off the connection part when the individual light emitting devices in the matrix arrangement are separated by cleavage.
In all of the above examples of production methods of semiconductor light emitting devices briefly described above, multiple semiconductor light emitting devices can be concurrently produced by concurrently forming structures of multiple semiconductor light emitting devices on a single substrate, and thereafter dividing the substrate into predetermined dimensions.
The semiconductor light emitting devices disclosed in JP 2000-091636 A, JP 10-173229 A, JP 10-107316 A, and JP 3117281 U have electrodes formed of metal, such as metal pad electrodes for wire bonding and metal thin-film electrodes formed on surfaces of the semiconductor lamination for current diffusion, respectively. In order to form such electrodes, the lift-off technique is used. That is, photoresist is applied over the entire surface of the semiconductor lamination on which electrodes are to be formed, and openings are formed by photolithography in the photoresist at positions at which the electrodes are to be formed. Then, a metal film is formed over the entire surface of the semiconductor lamination, and thereafter the portions of the metal film which are located on the remaining photoresist are removed by lift-off. Thus, the electrodes are formed at the predetermined positions.
In the case where the electrodes are formed by the lift-off technique as above, when the portions of the metal film are lifted off, the material constituting the electrodes causes migration and metal precipitates at various positions in the semiconductor lamination. Since the metal precipitated by migration can cause a short circuit between the n-type semiconductor layer and the p-type semiconductor layer, it is necessary to prevent migration to the greatest extent practicable. Therefore, the metals which are likely to cause migration, such as silver (Ag), have been considered not to be suitable for constituting electrodes.
On the other hand, since Ag is a material exhibiting high electric conductivity and high reflectance, there are strong demands for use of Ag as a material constituting electrodes in the semiconductor light emitting devices for the purpose of increase in the emission efficiency in the semiconductor light emitting devices.
According to the method for producing a semiconductor light emitting device disclosed in JP 2008-227018 A, migration of the materials such as Ag in the electrodes are prevented by forming the electrodes while the potentials of the n-type semiconductor layer and the p-type semiconductor layer are equalized by making a short circuit between the n-type semiconductor layer and the p-type semiconductor layer.
However, according to the method for producing a semiconductor light emitting device disclosed in JP 2008-227018 A, in order to prevent migration of the material constituting the electrodes, it is necessary to preserve the connection part equalizing the potentials of the n-type semiconductor layer and the p-type semiconductor layer until the final step in which the substrate is divided into the individual semiconductor light emitting devices. In addition, since the connection part is arranged between the adjacent semiconductor light emitting devices, the freedom of design of the structures of the semiconductor light emitting devices is limited. Consequently, there are demands for a production method which can achieve a higher degree of freedom of production steps and a higher degree of freedom of device structures.
In view of the above, the object of the present invention is to provide a method for producing a semiconductor light emitting device which can prevent migration during production and achieve a high degree of freedom of production steps and a high degree of freedom of device structures.